A Microsoft Band 2 fitness tracker. Scientists suspect people become overly dependent on such devices.
Photograph: Samuel Gibbs for the Guardian

They have become the must-have for fitness fans but wearable gadgets that track users’ physical activity may not help people lose weight, a new study has found.

Instead of motivating users to do more exercise over the day, the two-year survey found the devices were actually less effective at encouraging people to lose weight than simply following a diet and exercise plan.

Scientists suspect that people become overly dependent on the gadgets to help them change their health, developing a false sense of security – and would do better by relying on simple willpower.

Costing up to £150, the devices by technology firms including Fitbit, Jawbone and Misfit are worn on the wrist or arm, monitor physical activity, steps taken, calories burnt, heart rate and quality of sleep – and feed the data directly into a smartphone.

The researchers tracked 470 overweight or obese people, aged 18 to 35, for 24 months. Everyone in the study was put on a low-calorie diet, given an exercise plan and invited to regular group sessions.

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After six months, half the group was given a Fit Core armband, which tracks activity and feeds it into a computer programme that also allows people to log their diet. The other half were simply told to monitor their exercise and diet by themselves.

The group using the Fit Core gadgets lost an average of 7.7lb over two years, compared with an average 13lb in the self-monitored group.

A spokesman for Jawbone, which owns BodyMedia, the manufacturer of Fit Core, told the Daily Mail: “The results of the study do not suggest that wearable devices should not be used for positive weight loss outcomes.

“In fact, the study demonstrated positive weight loss in both groups. Wearable tech helps to bridge the gap between patients who have access to rather intensive weight loss treatments and the very many who don’t.”

A spokeswoman for Fitbit said: “The researchers point out that a limitation of their work includes the fact that they did not use a modern wearable device such as those offered by Fitbit. The upper arm device used in the study was limited to automatic data collection only.

“Most wearables today, including those offered by Fitbit, go far beyond data collection, offering individuals real-time access to their information, insights, motivation from associated social networks, and guidance about their health. We would strongly caution against any conclusion that these findings apply to the wearable technology category as a whole.”